Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
Many image sensors use reference currents to set operating points for various functional blocks. The reference currents may be generated based on one or more reference voltages, for example. Additionally, the circuits that generate the reference currents may conventionally include one or more resistors that provide a feedback voltage. The resistors, however, may be characterized as having large variation in resistance values, around 20% for example, which may affect the level of the reference currents. If the reference current is off from a desired level, the image sensor may not operate as intended.
Many techniques have been employed to mitigate the effects of the resistor variation of image sensor performance. However, some of these methods may not entirely eliminate the effects of resistance variation.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.